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Sorry to be picky but a 7DJ8 is not a direct replacement for a 6DJ8=6922. The 7 indicates it requires 7.6 Volts for the heater, while a 6DJ8 requires 6.3. So, does the mfr of your preamp say that 7DJ8 tubes can be substituted for the 6DJ8? If yes then wait for the tube to settle in. If no then get the correct tubes. Then let those settle in and tell us what you hear.
According to Kevin Deal at Upscal Audio the 7d68 is "...absolutely compatible with virtually any product that uses 6922 and 6DJ8 Whether it's an amp, preamp, CD player, whatever." You can see his video on this page. I'm using a 7dj8 miniwatt in my pre-amp instead of a 6dj8/6922; sounds great with no problems. It did take a day or too to fully burn in but it sounded pretty good right out of ther box. If in doubt contact Kevin directly.
This is one of the reasons Kevin is millionaire selling tubes, he is a nice guy, very friendly and a good neighbor, but compatible mean say just it works, just works, ie the tube will no explode.From 6,3V to 7,6V there is more than 19% less tension on the Cathode and people think it is all right.
7DJ8 / PCC88:This is an unusual tube that must have had a limited range of specific uses. It is virtually identical to the 6DJ8 except for the heater rating, which is 7 volts. I have seen Siemens, Valvo, Telefunken, Philips, Ultron and Matsushita (Japan) brands of this tube. It probably makes a good sub for the 6DJ8 and may last longer due to the higher voltage heater. Some are labelled with only the "PCC88" and others have both types listed on the label. All seem to be good quality. The Japanese factory was set up by Mullard, and these tubes even flash orange at the bottom of the filaments when first energized, like most European triodes do. Most of the European types were made at the Munich Siemens factory, the Hamburg Valvo factory, the Heerlen Holland Amperex Factory, or the Blackburn, UK Mullard factory. These sound just like the best 6DJ8 tubes, the German tubes being mostly neutral, and the Dutch and British tubes having a touch of midrange warmth. Watch for the very rare D-getter types and even rarer pinch waist types, often at bargain prices (compared to 6922 types in these categories) when you can find them. You may want to try a 7DJ8 for the longer heater life in a 6.3 volt circuit, and the lower price!Valvo 7DJ8: New Old Stock original Box. The 7DJ8 is identical to the 6DJ8 except for heater voltage. It will sub for the 6DJ8 and will give longer life. All are from Germany, 1960s vintage tubes with the large halo getter. These are very similar in sonics to Telefunken, and will generally outlast any other 6DJ8. A superb hifi tube at a savings.
Here's a backstory to this tube-Back in the 80's I had an Audio Research preamp that used 6922's or 6DJ8's. And I was well on my way into collecting tubes and figuring out how they sounded, why, and who really made them. I went down to an old parts store called Dow on Holt Blvd, in a crappy area of Montclair, California. But I'll go anywhere to get some cool stuff. While there I found some 6DJ8 in International boxes with tubes inside labeled "Made in Gr. Britain" I figured I scored as they must be from Mullard, Ediswan Electric, or Brimar. But upon furthur inspection I found no etched factory codes. Hmmm. They looked like Philips/Amperex/Mullard, at least internally. After some detective work I found they were made by National, also known as Matsushita in Japan. Eventually National became to be known as Panasonic. These have the early old National logo on the box with the little cardboard tube holder. Now I had seen many Japan 5AR4 and EL-34 labeled Made in Gr. Britain that were commonly thought of to be Mullard but were not. And anybody who knew them also knew that they were fantastic, well-made tubes. So I tried them. Heaven. They had a sense of ease and grace I associated with the best new old stock tubes in my collection. I figure how hard can they be to find? I went looking for them. One here, two there. I found a few in RCA boxes, again marked Gr. Britain, but that's about it. So they remained in my private stash and we have never found enough to test and grade into Gold and Platinum and offer for sale. Bummer. So before now we have never had these to offer to our customers.I recently found a small stash of them, and the heavens parted. My mind reeled back 20 years and I recalled how I felt when I plugged them in. They are PCC88, and as you know (or should know) they are a 7 volt perfect plug in substitute into literally every product using 6DJ8 or 6922's. The sound? I used them here in a Cary SLI-80 Signature F1 and it was just like I remembered. The midrange is similar to a real Telefunken 6DJ8, but with better extension on top and bottom. There is a sense of humanity that is exhibited by the best in new old stock (NOS) tubes. I was at one point suggesting these for Audible Illusions preamps. Then I had a guy with a failure we warranted, and thought it was a bad move. THEN I got a call from a guy that said the Matsushita’s were “The best thing that ever happened to my preamp” referring to his L-1, and that they lasted for years. And another guy that wrote a review saying it was that good. So I guess that we will say party on guys. Look. I love the super expensive stuff. Everybody deserves to own some at some point. But here is an opportunity to get something truly vintage, truly rare, and very sexy that sounds incredible for low $$$ considering you get our grading process. Buy these along with another type or two and have a blast. Have your own awakening.
So, does the mfr of your preamp say that 7DJ8 tubes can be substituted for the 6DJ8? If yes then wait for the tube to settle in. If no then get the correct tubes. Then let those settle in and tell us what you hear.
Some datasheet say 7.0V others say 7.6VSeems there is two types of 7DJ8.7DJ8 RatingsVh Ih Cgk Cak Cga7.6 0.3 3.3/6.0 1.8/0.18 1.4/1.4http://tdsl.duncanamps.com/show.php?des=7DJ8http://www.revoco.cz/data/datasheets/tubes/6dj8.pdf
Have you tried Herbies tube dampers? I've found them to perform quite well in improving tube performance by reducing vibrations that can impact transparency, sound stage depth and bass among others. Highly recommended.
The P- series have filements for 0,3A! So depending on tube it has different voltages and always the same current.All those people listening to p-serie tubes in equipment for e-serie tubes (6,3V filements) don't take there amplifiers and listening serious. But if they want to waiste there time and money.....
Your point is well taken. When it comes to tube substitution, the best source of information is the manufacturer. I acknowledge in this instance, I took Kevin's word on it and didn't check with manufacturer; I have just sent the manufacturer an e-mail. I'll let you know what he says. But I would add that it's one thing to diasagree but it's another thing to be disagreeable. When we begin to denigrate the values or intelligence of others, we are, in my opinion, heading out of bounds. The precesence of civility and courtesy is what makes Audio Circles a much better forum than the Audio Asylum. Just my 2 cents. Happy listening all.
It is not needed to send an email to the manufacturer of the amplifier because we already have the right information from the manufacturer of the tubes. And it is clear that the 7dj8 can not be on the place of an 6dj8 unless you change the heatervoltage.If you want to make this a better forum you have to accept some physic laws. It's not a matter of that i like green and others red.
